As demand for high performance devices grows, an increasing number of transistors are packed into a single integrated circuit chip. To fit increasingly more transistors on a single chip, the size of the transistors has been continuously reduced. In a planar polysilicon transistor, as the size of the transistor shrinks, the distance between the source and drain is reduced and it becomes increasingly difficult for the gate to control the flow of current through the transistor.
Fin field-effect transistors (FinFETs) have been developed in an attempt to solve this problem by wrapping the gate around a silicon “fin” structure. Compared to conventional planar transistors, this structure allows the gate to have a better control over the flow of current. Generally, to form a gate structure in a transistor (i.e., a planar transistor or a FinFET), a polysilicon layer or metal layer is disposed over a dielectric layer such as silicon oxide.
Metal gates are often used with high-k dielectric layers to form transistors known as high-k metal gate (HKMG) transistors. Compared to polysilicon gate oxide transistors, HKMG transistors may exhibit lower current leakage. However, even though HKMG transistors may reduce overall current leakage in an integrated circuit device, they generally offer fewer levels of gate oxide thicknesses compared to polysilicon transistors (e.g., transistors with polysilicon gate structures).
Generally, HKMG transistors may offer only two gate oxide thicknesses to support two different voltage levels (e.g., low voltage high performance gate oxide and high voltage gate oxide). However, circuitry within an integrated circuit device may require more than two different operating voltages. As an example, different circuit elements in the integrated circuit device may operate either at a low, medium, or high voltage level.
As the thickness of the oxide layer is varied to accommodate devices operating at different voltages, an integrated circuit device with triple gate oxide (TGO) devices, or transistors with three levels of oxide thicknesses, may thus allow better voltage control.